Minor readme issue

[eddyjlsh]

The readme has a typo for the docker instructions to run a node.

./scripts/build-manga-node-docker-image.sh misspells mangata, it should be ./scripts/build-mangata-node-docker-image.sh.

[goncer]

@eddyjlsh plz update it and create a PR :)

[gleb-urvanov]

Resolved #110